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Etching method and apparatusEtching method and apparatus description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070019206, Etching method and apparatus. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to Japanese Patent Application No. JP 2005-208589, which was filed on Jul. 19, 2005, the contents of which, are incorporated herein by reference, in their entirety. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an etching method and apparatus for etching a multilayer film formed by crystal growth on a substrate. [0004] 2. Description of the Related Art [0005] The demand for better semiconductor device characteristics has been growing year by year, and consequently the need for higher processing precision has been accelerated more than ever. For example, the processing precision is also required to be high for the etching depth at the time of etching a layer to be etched. [0006] For improvement of the processing precision as to the etching depth, a related technology describes the etching method using a layer for use to detect an etching endpoint, i.e., a so-called etching stop layer. With this etching method, first of all, a semiconductor substrate is formed thereon with a layer of a predetermined thickness for use to detect an etching endpoint. This layer has the index of refraction higher than the semiconductor substrate. On such an etching endpoint detecting layer, another semiconductor layer is then formed with the index of refraction lower than the etching endpoint detecting layer so that a mask is formed. The resulting layer formation is then exposed to laser light of a predetermined wavelength, and the reflected light is monitored. During such monitoring, the etching operation is stopped when the etching endpoint detection layer is detected. For more details, refer to Japanese Unexamined Patent Publication JP-A 8-181387 (1996), for example. If for dry etching, there is an etching method of forming a layer called marker layer having a different composition ratio, and stopping the etching operation when the marker layer is detected. [0007] Another related technology describes an etching apparatus that calculates the etching depth based on the frequency distribution as a result of frequency analysis using the maximum entropy method. In this etching apparatus, an etching object is exposed to coherent light, e.g., laser light, and the frequency analysis is conducted with respect to signals as a result of interference of light due to the light reflection on the surface of the etching object. From the result of the frequency analysis, the etching speed is calculated for use as a calculation basis for the etching depth together with the time taken for the etching operation. This method allows monitoring of the etching depth even when the etching object has no base such as substrate, and enables to stop the etching operation when the etching reaches any desired depth. For more details, refer to Japanese Patent No. 2545948, for example. [0008] The problem with the technology is that the etching depth may not be calculated with precision because the interfered light is distorted periodically at a specific phase. For the purpose of solving such a problem, further another related technology describes a method of detecting the etching depth. In the method, an etching object is exposed to light varying in wavelength so that the etching depth is calculated. By exposing the etching object to light varying in wavelength as such, the interfered light can be plurally detected. Accordingly, even when one interfered light is distorted at a specific phase, another interfered light can serve as a complement thereto so that the etching depth can be detected with precision. For more details, refer to Japanese Unexamined Patent Publication JP-A 2001-210625. [0009] With the related technologies, the etching depth of the layer to be etched is calculated even when the layer to be etched has no base such as substrate based on the etching speed and the time taken for the etching operation. The etching speed is derived from the frequency of the interfered light as a result of light reflection on the area covered by the mask, i.e., the area not to be etched, and the light reflection on the area not covered by the mask, i.e., the area to be etched. [0010] For etching of an etching film configured by a plurality of layers to be etched varying in index of refraction, i.e., multilayer etching film, the etching depth may be measured prior to etching using the interfered light generated due to light reflection on boundaries between the layers to be etched. FIGS. 7 and 8 both show such an exemplary method of measuring the etching depth using the interfered light generated due to light reflection on the boundaries between the layers to be etched. [0011] FIG. 7 is a schematic diagram showing the configuration of an etching apparatus 3 in a related technology. The etching apparatus 3 includes a light source detector section 14, a dry etching chamber 20, and a control section (not shown). The light source detector section 14 includes a light source for emitting light such as laser light, and a detector for receiving a reflected light 50. The reflected light 50 is the light emitted from the light source, and reflected by a to-be-etched substrate 30 being an etching object. The dry etching chamber 20 dry-etches the to-be-etched substrate 30 disposed therein. The control section measures the etching depth based on the frequency of an interfered light found in the reflected light 50 received by the detector in the light source detector section 14. The dry etching chamber 20 includes a light transmitting window 21 that passes therethrough an incident light 40 coming from the light source in the light source detector section 14, and the reflected light 50 as a result of reflection on the to-be-etched substrate 30. [0012] The incident light 40 coming from the light source detector section 14 passes through the light transmitting window 21, and the incident light 40 illuminates the to-be-etched substrate 30 disposed in the dry etching chamber 20. The incident light 40 illuminating the to-be-etched substrate 30 as such is reflected by the to-be-etched substrate 30, and the resulting reflected light 50 passes through the light transmitting window 21, and reaches the light source detector section 14. The reflected light 50 is then received by the detector in the light source detector section 14. [0013] FIG. 8 is a diagram showing the cross section of the to-be-etched substrate 30 shown in FIG. 7. The to-be-etched substrate 30 is configured by an layer to be etched 32 formed on a substrate 31. The incident light 40 is the one directed from the light source detector section 14 shown in FIG. 7, and the incident light 40 illuminates the layer to be etched 32. The incident light 40 illuminating the layer to be etched 32 as such is partially directed to the layer to be etched as an incident light 40a, and the remaining portion thereof is reflected by an etching surface 33. The incident light 40a directed to the layer to be etched as such is partially directed to the substrate 31 as an incident light 40b, and the remaining portion thereof is reflected, as a reflected light 50a, by a boundary 34 with the substrate 31. Although FIG. 8 shows only one layer to be etched, the boundary 34 with the substrate 31 is presumed as a boundary between the layers to be etched. [0014] In the reflected light 50, the reflected light as a result of reflection on the etching surface 33 is overlaid with the interfered light, i.e., as a result of interference between the incident light 40a to the layer to be etched, and the reflected light 50a on the boundary 34. The detector in the light source detector section 14 receives the reflected light 50, and to the control section, outputs an electric signal being a conversion result of the received reflected light 50. The control section observes, i.e., monitors, the electric signal coming from the detector, and calculates the etching speed from the frequency of the interfered light found in the reflected light 50. In this manner, the etching depth is measured. [0015] The issue here is that the etching method of the related technology is using an etching stop layer. The use of an etching stop layer has several drawbacks of imposing restrictions on the chemical solutions, the etching gas, and the etching requirements, complicating the process, and causing variations to the etching amount except for the etching depth, for example. The use of the etching stop layer also adds constraints to the device designing, whereby it is highly likely to adversely affect the device characteristics. [0016] With the related technologies, the etching speed is calculated from the frequency of an interfered light for use as a calculation basis for the etching depth. This advantageously increases the calculation precision for the etching depth. Such related technologies, however, are using the reflected light on the area covered by the mask, i.e., mask pattern. When the pattern area is small in the mask, the reflected light on the mask pattern will be thus reduced in intensity, and the intensity of the interfered light will not be enough, either. [0017] The method shown in FIGS. 7 and 8, i.e., the method of etching a multilayer etching film varying in index of refraction with the etching depth measured by the interfered light as a result of light reflection on the boundary between the layers to be etched, is not dependent on the use of a mask. Considered here is a case, with the method, of forming a plurality of layers to be etched by crystal growth on a substrate. In this case, the nonuniformity of crystal growth may vary the thickness of the layers to be etched. When the thickness of the layer to be etched reaches the value defined by a specific relational expression for the wavelength of the incident light, the incident light entering the layer to be etched is cancelled out by the light reflected on the surface opposite to the incident-light-receiving surface so that no interfered light is generated. With this being the case, the etching speed cannot be calculated because no interfered light is available for monitoring. The etching depth cannot be thus measured. SUMMARY OF THE INVENTION [0018] An object of the invention is to provide an etching method and apparatus that are not dependent on the use of a mask, and are capable of measuring the etching depth even when layers to be etched vary in thickness due to the nonuniformity of crystal growth. [0019] The invention is directed to an etching method for etching a plurality of layers to be etched having a different index of refraction. In the etching method, the layers to be etched are illuminated by two coherent lights each having a different wavelength, and two interfered lights generated by the illuminating two different lights reflected on a boundary between the layers to be etched are observed. Based on the frequency of either of the two observed interfered lights whichever meeting predetermined requirements, the etching depth is measured. [0020] According to the invention, for etching a plurality of layers to be etched varying in index of refraction, the layers to be etched are illuminated by two coherent lights each having a different wavelength, and two interfered lights generated by the illuminating two different lights reflected on a boundary between the layers to be etched are observed. Based on the frequency of either of the two observed interfered lights whichever meeting the predetermined requirements, the etching depth is measured. [0021] As such, the layers to be etched are illuminated by two lights each having a different wavelength, and two interfered lights generated by light reflection on a boundary between the layers to be etched are observed. Based on the frequency of either of the two observed interfered lights whichever meeting the predetermined requirements, the etching depth is measured. Accordingly, even when one of the interfered lights is not observed, the remaining interfered light is available for observation. This thus enables to measure the etching depth based on the frequency of the interfered light. Continue reading about Etching method and apparatus... Full patent description for Etching method and apparatus Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Etching method and apparatus patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Etching method and apparatus or other areas of interest. ### Previous Patent Application: Spectrometer based multiband optical monitoring of thin films Next Patent Application: Condition assessment system for a structure including a semiconductor material Industry Class: Optics: measuring and testing ### FreshPatents.com Support Thank you for viewing the Etching method and apparatus patent info. IP-related news and info Results in 0.33782 seconds Other interesting Feshpatents.com categories: Medical: Surgery , Surgery(2) , Surgery(3) , Drug , Drug(2) , Prosthesis , Dentistry 174 |
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